computer wont start??

turned on pc all lights are flashing both pcu fan and power pack fans are running. pc monitor lights come on flashing green then go to amber. nothing on the screen, blank. monitor works tried it on another pc, did some reading changed the ram, both slots, also changed graphic cards, and also tried a different hard drive. the only thing i have'nt changed or checked is the mother board,any one got any ideas pleaseEddie

hi thanks all tried safe mode still nothing, removed cmos battery even tried another battery, and yes the monitor is plugged in correctly its also colour coded and have just tried another psu still nothing. one minute its ok shut comp down when i next tried to start nothing, so do i now suspect motherboard in which case looks like a trip to the tipEddie

Ive got a problem whereas my laptop will not boot up properly. On opening itasks how id lik to start up....Safe mode, Last know good config, Normally etc etc, ive tried all of them, but it keeps bringing me back to the same screen (How id like to start up) Im running windows XP which it tries to start (ie, scrolling bar across the screen) like its gonna work, but then back to the same screen.